Liquid, pigmented coating agents are conventionally produced using a base formulation, in which the pigment(s) is (are) ground in the binder or in a special paste resin. The finished coating agent is formulated by mixing the base formulation with a proportion of an additional binder component and optionally, any other additional constituents may be added.
Another conventional alternative for the production of liquid, pigmented coating agents is to use a paint mixing system in which liquid coating agents having different colors are mixed together to yield the liquid coating agent with the desired pigmentation or desired color shade. The different color liquid coating agents are per se finished compositions, i.e., ready to apply compositions.
A further alternative is production by mixing components, wherein at least one of the components to be mixed is not per se a finished (ready to apply) coating agent. For example, the coating agent, which is pigmented as desired, may be produced by mixing pigmented and optionally, unpigmented semi-finished products or by mixing a per se finished coating base with one or more pigment pastes (tinting pastes).
In industrial mass-production coating with pigmented liquid coatings, for example, in automotive original coating, many coating layers are applied in more than one color shade, i.e. with different pigmentation. For example, in automotive original coating, in particular, the primer surfacer or base coat layer are applied in a number of different color shades corresponding to the color shade range, wherein the various pigmented primer surfacer or base coat coating agents are each applied from a separate circulating line. The number of circulating lines for coating agents in standard color tones is here limited for logistical reasons. Applying coatings of special color tones in addition to the coatings in standard color tones can only be achieved with considerable additional effort.
DE 101 07 951 A1 describes a process for coating a substrate in a specified mixed color tone, wherein the coating is produced in the desired mixed color tone by means of a mixing apparatus in the flow path upstream from an application unit and is then applied onto the substrate.
The process according to DE 101 07 951 A1 overcomes the above-stated logistical problem and also makes it possible to achieve integration of coating agent production virtually into the coating application process. However, in many cases, the degree of mixing of the applied coating agent is in need of improvement. Moreover, the process can only be used with components that are readily miscible with one another.
The process according to the invention described below not only provides an alternative solution to the process of DE 101 07 951 A1, but also provides an improvement in the resulting coating since the applied coating agent has an extraordinarily good homogeneity. The process according to the invention is also usable in those cases in which the coating agent is formed from components which, by their nature, can be mixed together only with difficulty and with particular effort. For example, components may be difficult to mix together if the components to be mixed have relatively different properties, for example, different density, viscosity and/or polarity/nonpolarity. The quality of a coating applied from a coating agent produced by mixing two or more components with regard to technical and/or optical properties is dependent upon the degree of mixing of the components before application. It is generally known that greater homogeneity of such a mixture, for example, finer dispersion, is accompanied by an increase in the quality of the coating applied therefrom.